This invention relates to dismantlable torsion bar assemblies, and particularly to anti-roll bar assemblies for use in rail vehicles and other heavy load applications.
A torsion bar, such as an anti-roll bar (hereafter “ARB”), is a bar which is mounted for rotation through a small angular range so as to transmit torque between, usually, a pair of torque transmitting elements (hereafter referred to as “levers”) which are typically but not necessarily short arms extending radially outwardly from the respective ends of the bar. Such assemblies are typically subjected to frequently and rapidly reversing loads, which in ARBs for passenger-carrying rail vehicles can give rise to a torque of the order of about 20 kNm, with the bar being typically around 65 mm in diameter.
Since the torsion bar must pass through the structural components of the bogie, it is necessary to assemble at least one of the levers in-situ after mounting the bar in the bogie. The ARB assembly must fit within a limited space envelope, with the axial length of the bar being constrained by the track gauge. Much effort has therefore been expended in devising a means of connecting the lever to the bar which allows the joint to be made and unmade with the ARB in-situ in the bogie and which is capable of reliably transmitting such heavy loads without unacceptably increasing the size and cost of the assembly.
A common solution to this problem comprises a cylindrical splined joint as shown for example in WO 2004/091992 A1. The splines permit the arm to be assembled by push-fitting onto the bar; disadvantageously however, the joint is subject to backlash under reversible loads. Moreover, stress concentrations in the splines require the end regions of the bar to be diametrically enlarged in order to avoid fatigue failure, which is undesirable since it significantly increases the cost of the bar. In order to reduce these problems, conical splined joints have been developed, which however are considerably more expensive to manufacture. Moreover, it is found that the splines wear in service, which requires the ARB assembly to be replaced several times during the life of the bogie.
It is also known to assemble the levers to a heavy duty ARB by means of a shrunk or pressed cylindrical interference fit, which is advantageously free from backlash, relying on the frictional force developed by the pressure and the coefficient of friction between the mating dry steel surfaces to transmit torque between the respective parts. Such ARB assemblies are advantageously compact, low in cost and largely free from stress concentrations. However, the assembly of the joint requires either that the levers are heated to a high temperature, which is hazardous and inappropriate in rail maintenance depots, or the application of a very heavy press force, which it is impractical to react against an ARB in-situ in a bogie.
GB 1 381 699 depicts an ARB assembly for a rail vehicle bogie in which the lever is split to form a splined clamp which engages the end of the ARB. Clamped, splined cylindrical joints of this general type have been used successfully on lighter, underground rail vehicles, and advantageously allow the clamp to be tightened in-situ so as to reduce or remove backlash as the splines wear in service. However, such joints have not been proven for use in heavier applications such as standard overground passenger-carrying rail vehicles, and doubts exist as to their load-carrying capacity.
An alternative approach is to provide a locking collar as a separate component which is engaged between the lever and the ARB. Known joints of this type have been found suitable for in-situ assembly and disassembly, but disadvantageously tend to be complex and bulky.
It is an object of the present invention to provide a dismantlable torsion bar assembly which is more suitable for use in heavy load applications requiring in-situ assembly, and particularly for use as a rail vehicle ARB assembly. It is a further object to provide a corresponding method of assembly. In accordance with the present invention there are provided respectively a dismantlable torsion bar assembly and a method of assembly, as defined in the claims.